1. Field of the Technology
The present disclosure relates to digital printing systems having plural tandem marking or printing engines of the type with seamed photoreceptor (P/R) belts. In such printing systems, it is common practice to invert the sheet after marking on one side in a first printing engine and for feeding the inverted sheet into a second printing engine for marking on the opposite side of the sheet to thus facilitate high speed duplex digital printing. In printing systems having plural tandem engines using photoreceptor belts with seams, it is necessary to avoid imaging on belt seams. This requires some manner of skipping pitches in order to avoid placing images on belt seams. However, skipping pitches adversely affects printer efficiency.
2. Description of the Prior Art
A general manner of belt synchronization to avoid seams, showing the control of the belt speed of the marking devices to synchronize belts, is disclosed in U.S. No. Pat. 7,519,314 B2, assigned to the same assignee as the present invention. However, this technique is relatively inefficient in relation to the present disclosure. It is also shown in pending U.S. application Ser. No. 12/388,101, filed Feb. 18, 2009, now Publication No. 20100209161, by Ana P. Tooker et al, “Controlling Sheet Registration In A Digital Printing System”, assigned to the same assignee as the present invention, to control sheet registration in a printing system by varying the dwell time of a sheet in an inverter in a first marking device and changing various transport motor speeds to time the arrival of the sheet at a second marking device. However, there is no disclosure of the need to synchronize the belts for efficient avoidance of belt seams for the productivity of the printing process. With the speeds of the two PR's no longer synchronized, the seam zones of said PR's are no longer in phase. With no understanding of the relative position of the two seam zones to each other, skipped pitches may occur in a non-optimal manner impacting customer productivity. Seam synchronization is also shown in U.S. application Ser. No. 12/491,307, Publication No. 20100329742, now abandoned, assigned to the same assignee as the present invention, filed Jun. 25, 2009 by Andrew James Bonacci et al, “Controlling Sheet Synchronization in a Digital Printing System”; and U.S. Continuation-in-Part application Ser. No. 13/225,744, filed Sep. 06, 2011 of the same title, by the same inventor and assigned to the same assignee as the present invention. However, neither this application nor the prior art accounts for efficient spacing of images on PR's to adjust to different image sizes or print sheet sizes in the printing system.